What moments and averages does ASTRA report? - WKB319098

ENVIRONMENT

• ASTRA
• Software: ASTRA
• Instruments:
  • Light Scattering Detectors: LS 11 (18 angles), LS 5 (8 angles), LS 2 (3 angles)
  • UV Detector (channel 1 only)
  • RI Detectors: Optilab and third-party RI detectors

ANSWER

To calculate signal-to-noise (S/N) ratio in ASTRA, use the USP <621> method: divide peak height (H) by peak-to-peak baseline noise (h). ASTRA can automatically calculate h for LS and Optilab RI detectors using diagnostic methods. For UV and third-party RI detectors, h must be estimated manually from baseline signal oscillations. Peak height (H) is available in the ASTRA Report Designer under peak statistics. A minimum S/N of 100:1 is recommended, with higher ratios needed for sensitive applications.

ADDITIONAL INFORMATION

In the table below, the relevant molar mass and radius moments that should be reported in ASTRA are provided. Light scattering in principle provides the weight-average molar mass and z-averaged RMS radius.

Pay particular attention to nomenclature. For molecular weight, terms like MW, Mw, molecular weight, molar mass are all used interchangeably. Light scattering provides theweight-averaged molecular mass(Mw). Likewise, for the RMS radius, radius of gyration (Rg or rg) is also commonly. The RMS radius and Rg refer to the same value, which for light scattering is thez-average RMS radius. ASTRA calls this "rz". 

Please seeTN3507 - Moments and Averages Reported by ASTRAfor additional information regarding molecular standards. This can be found on the Wyatt Customer Support Center at https://www.wyatt.com/support.html